Sagan assembled a committee to collaborate on the project. After much deliberation with various clever people, scientists and (ahem) science fiction authors as to what sort of content would be appropriate, it was realised another plaque would be insufficient. The committee decided to record a kind of multimedia presentation of Earth civilisation and environment on a 12-inch phonograph record and send a copy with each of the Voyager spacecraft.

...I send greetings on behalf of the people of our planet. We step out of our solar system into the universe, seeking only peace and friendship. To teach if we are called upon, to be taught if we are fortunate. We know full well that our planet and all its inhabitants are but a small part of the immense universe that surrounds us and it is with humility and hope that we take this step.- Kurt Waldheim, U.N. Secretary General

The committee then set out to gather and compile the content, with about six months in which to do it. The result was a collection of images and sounds of many Terran people and cultures, as well as recordings of 'natural' sounds like surf, thunder, rain and the calls of many different animals. Spoken greetings were included in 55 different languages including Cantonese, Sotho, Rajasthani and Sumerian as well as English and other European languages, preceded by the above spoken message from the U.N Secretary GeneralKurt Waldheim.

The majority of the greetings were from people of no particular stature in their culture; often people native to the desired culture were found by a 'friend of a friend' approach. Swahili dialogue was unfortunately omitted because the speaker cancelled at the last minute. Linda Salzman Sagan, tasked with gathering these recordings, responded to the first criticism of many (how much more difficult it would be for extraterrestrials to interpret 55 different languages instead of one or two), noting that:

"[The committee compiling the record] were aware that [sending greetings in one or two languages] might have given the extraterrestrials a better chance of understanding the words precisely, though it would have raised the thorny question of which two languages to send. We felt it was fitting that Voyager greet the universe as a representative of one community, albeit a complex one consisting of many parts."

The record itself was made of gold-plated copper - the copper being similar to the mother for a standard vinyl LP. The metal was used for longevity, always a prime concern with such limited means of interstellar travel. The audio was recorded as normal although the standard 33RPM speed was roughly halved to 16 2/3 RPM, increasing playing time to almost two hours at the expense of some fidelity.

Imagine...If another civilization out there were to hear this, they would think: "What a wonderful place the earth must be." I would want this to be the first contact with another life form.-dialogue from The X-Files, written by Glen Morgan & James Wong

This is a present from a small distant world, a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.- Jimmy Carter

A total of 122 images were recorded on the disc, including many pages of text. The range of subjects was huge, from a nursing mother to a schoolroom and several well-known landmarks or buildings including Sydney Opera House and the Great Wall of China. Also recorded were a written message from U.S. PresidentJimmy Carter and four pages of text listing the members of Congress involved in committees relating to the Voyager project (it has been suggested, not unreasonably, that this record was compiled to appeal as much to the humans that sent it as to the potential recipients).

Each image on the record took up about 12 revolutions. Of the 122 images, about 20 were in colour. Colour was achieved by recording every colour image three times in succession, one greyscale image each for the red, green and blue portions; this gave a combined colour depth of 12 bits or 4096 colours (individual image depth was 16 shades of grey, or 4 bits). Combining the three would give the original image.

The first colour image was of the solar spectrum, intended as a calibration tool so the viewer could establish colour settings for viewing the rest of the colour images. It was believed any species capable of intercepting either Voyager probe would understand a solar spectrum.

Greetings to our friends in the stars. We wish that we will meet you someday.- Translated greeting in Arabic

Of equal importance to the content of the record were the instructions for playing it. Any discussion of the effectiveness of the content is academic if it will never be seen or heard. For the ignorant "end user", playing the audio portion is relatively simple - the record was to be supplied to infinity with a cartridge and stylus so only a means for stably rotating the record and holding the stylus in place were needed (as well as a gaseous environment).

The process of reading and decoding the images proved more difficult to explain and the authors will probably never learn whether they were successful or not. Instructions for playing the record as well as interpreting and decoding its contents were designed, adorning the gold-plated protective aluminium casing of the record. The instructions took the form of seven diagrams, described in the following sections (warning, this gets a bit techie).

Hydrogen transition diagram

A key reference for decoding the rest of the diagrams.

This is one of two diagrams that also appear on the Pioneer plaques. It is a key for the rest of the diagrams, although unfortunately there would be no way of getting the reader to look at it before any of the other diagrams. Decoding this would give the reader the requisite information to decode the rest of the diagrams.

It depicts a hydrogenatom in its two lowest states, intended to illustrate the binary numbering system that is used throughout the other diagrams. A '|' is shown between the two atom diagrams indicating that the length of a transition from one state to another should equal a single unit. Binary was chosen here because it assumes nothing (for example, the amount of appendages that the reader might use to aid arithmetic) and is the simplest known numbering system. It was felt that any race familiar with the most abundant element in the universe would be able to understand this.

The main intent here was to establish the importance of the assumed knowledge on the part of the reader, of the exact time a hydrogen atom takes to oscillate between its two lowest states, which is 0.7 billionths of a second or more precisely, 7.04024183647-10 seconds. This information is vital in decoding other parts of the instructions.

Record plan view

Instructions for setting up and playing the record.

This diagram shows a view of the record from above with the stylus cartridge in the starting position for playing, hopefully implying that it should be played from the outside inwards (though the direction of rotation is not marked - presumably it was thought this could be inferred by looking at the spiral pattern on the outer or inner edge of the record). The binary number 100110000110010000000000000000000 (shown as '|'s for 1s and '-'s for 0s) is printed anti-clockwise around the outside of the record diagram: 5,113,380,864 in base 10. Multiplied by 7.04024183647-10 this gives 3.599, the amount of seconds a single revolution of the record takes.

On first inspection (or more likely, my first inspection) this seems heavily reliant on our units of time, but recall that it relates to an absolute constant: the time for a single oscillation of a hydrogen atom. Therefore the units of measuring time employed by the "user" are irrelevant if they are capable measuring the said oscillation.

This diagram again shows the record set up for playing but from the side, again with the stylus cartridge in place. Underneath this, enclosed with two vertical bars, is the binary number 1000010110000000000000000000000000000000000, which is 4,587,025,072,128 in base 10. Going back to our earlier primer, 7.04024183647-10, and multiplying the two we get 3229.377 seconds, the total playing time (53.8 minutes) per side.

Picture signal diagram

Detail on identifying and decoding the picture signals.

This is where textual limitations start to press. This diagram depicts three waveforms that each generate a single line of an image, preceded by a regular waveform: very roughly, "\/\/\/\/\/\/\" only much taller and tighter. The intention here is to show that the waveforms for images are very similar to each other and that the data for each image is 'framed' by a symmetrical waveform as described. To show that the image lines follow each other, each of the three waveforms has a sequential binary number above it, from "|" to "||".

The first of these waveforms has the binary number 101101001100000000000000 under it, between vertical bars that clearly mark the start and end of the waveform. The binary number is 11,845,632 in base 10, which multiplied by our constant, 7.04024183647-10, gives 0.0083396 or about 8 milliseconds: the correct time for rendering a single picture line.

A further illustration below these waveforms aims to show how the complete picture is to be built up. An exaggerated reproduction of the diagram follows:

It helps in understanding this diagram to remember that the picture lines are vertical, not horizontal as with modern television sets. Each downward slope represents a single rendering pass, and each upward slope represents the vertical retrace interval. Each pair of circles represents the start and end of a rendered line. The operation is thus:

Downward pass: line 1 drawn

Upward pass: scanner returns to the top

Downward pass: line 2 drawn

Upward pass: scanner returns to top

Downward pass: lines 3 drawn
etc, etc...

*hairline recedes visibly*

Picture composition diagram

A symbolic representation of a complete image.

This diagram shows how an image is built up, illustrating how many scanlines make up a complete image (512). A rectangle with a regular up-down zigzag pattern from the top to the bottom indicates the motion of the picture rendering.

The majority of the rectangle is left blank but a single up-down trace on the far right of the rectangle indicates the last scanline; above this the binary number 1000000000 is printed vertically. This is 512 in base 10 and indicates the number of scanlines in a complete image.

On the top left of the rectangle is the binary number 10000, which is 16: the number of shades of grey in each scanline. This information is not needed to read the image.

An aid for the "user" to see if they are reading the images correctly.

This diagram shows the very first image on the record: a perfect circle. The image is included for the purposes of calibration. The reader would compare the first image they render from the record, against this image. If the circle appears distorted or garbled, the rendering needs to be adjusted. Once this circle correctly displays, the reader's rendering equipment is set up to accurately draw the remaining images.

Pulsar map

A representation of the source of the spacecraft.

This is a scale drawing showing the position of Sol in relation to fourteen pulsars in our galaxy. This is shown as a series of 'spokes' radiating from a central point, representing Sol. Each of these spokes points to the position of one of the fourteen pulsars and has a binary number along it, representing the pulse frequency of that pulsar. It is thought that Species that might intercept either Voyager spacecraft would be familiar with measuring the intervals of pulsars. A single spoke, longer than all of the others with no binary notation on it, points from Sol to the centre of the galaxy.

Hello from the children of Planet Earth.- Greeting in English

The critical assumption made here is the possession of the power of sight by the interceptor, but in the designers' defence it's probably a safer bet than using braille instructions or something.

The final thing notable about the record casing is that it is electroplated with depleted uranium, the decay of which is intended to act as a clock of sorts, indicating how long the Voyager craft has been in space if it is ever intercepted. Uranium 238 has a half life of 4.51 thousand million years so any recipient can measure the amount of U-238 left and calculate the time it has been in space (as long as they're not hypersensitive to alpha particles or something, in which case they would have done pretty damn well to survive long enough to get into space).

Both Voyager spacecraft were launched in 1977. In 1990, after relatively brief tours of the outer gas giants (Jupiter, Saturn, Uranus, Neptune), they both passed the orbital path of Pluto essentially leaving the solar system. Voyager 1 is travelling at roughly 3.6 AUs per year, Voyager 2 at about 3.3. Voyager 1 overtook Pioneer 10 as the most remote manmade object in the universe in February 1998 and at the time of writing is about 12.8 billion kilometres from Earth.

Although decidedly far removed from the public eye (until I researched this writeup I thought both spacecraft were dead, like Pioneer 10), both spacecraft are very much alive and still support daily communication sessions with the Deep Space Network. They are expected to continue operating until about 2020; until then they continue to report on their surroundings and are now part of a project to discover where the termination shock of the solar system is.

The gold records on both Voyagers are expected to last one thousand million years or more in deep space, barring damage. This is just as well because it will be approximately forty thousand years before Voyager 1 passes within two light years of another star (AC+79 3888, in the Camelopardalis constellation). Voyager 2 will come within five light years of Sirius after about 296,000 years of stellar wandering, though bear in mind that is further than Sol is from its closest neigbhour. Beyond that it is difficult to determine where either spacecraft will go with as much certainty.

The spacecraft will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space. But the launching of this bottle into the cosmic ocean says something very hopeful about life on this planet. - Carl Sagan

The following is a complete contents listing of the Voyager Golden Record, as recorded on nasa.gov:

WRT the fourth diagram in the 'tech' section above: if anyone can explain to me why the vertical scanlines are staggered on the diagram I would appreciate it. A photograph of the original drawing is at <http://www.cedmagic.com/featured/voyager/waveform.jpg>